rev. 7-24-2024
A few loaners round out the field...
... which led to more 1/3-scale models (not factory authorized, but as faithful as I could make them). Cone, Shark, Delta, Galerider, Seabrake.
Interestingly, the 1/3-scale models behave exactly like their big brothers. Drag is proportional to cross section, so the models product 9 times less drag. Drag ~ velocity^2 up to 14 knots, the limit of our testing. They also have very similar surfacing behavior, which lead to the premise that testing these with scale rode in Force 7 conditions, with steep waves and a little engine assist, is equivalent to gale conditions with a full scale drogue. Instead of loads approaching a ton, they stay below 150 pounds, and hand-over-hand recovery is 5-20 pounds instead of 50-200 pounds; makes a real difference when there are 100-300 feet of line out! The result is practical testing at more speeds and with more combinations, allowing full-scale testing to focus on the right questions.
I since made a few scaled to my F-24 trimaran, primarily for emergency steering experiments . In proportion, they perform right in between their big and little brothers. Very scalable.
If you want to try DIY, the Delta Drogue is by far the simplest. Basically, it is a triangle of fabric of the dimensions of the model number (a Delta Drogue 72 is made from a triangle 72inches on a side). Cut about 20% of the length off each corner, rim the fabric with strong webbing, and then sew the edges together up into a balute (Google it) with about 50% of the edge sewn and 50% open (there shdould be three long slots for the water to blast out). The webbing along the sides should be long enough (about 50% of the length of a side before cutting) to joint at the apex. Complicated to describe, but easy to fabricate.
After testing full scale drogues at speeds up to 7.5 knots and confirming scalablity, I built a universal cross reference table (Practical Sailor) so that you can pick a drogue for your boat, whether for steering or speed reduction. Generally it agrees with manufacturers, but they often have different theories regarding how much drag is best.
Now I am starting to focus on tandem drogues; does it make sense to trail 2 drogues on the same rode, as conditions get worse? The answer seems to be a resounding yes. Unlike anchors where rode forces destabilize anchors, in this case they seem to stabilize each other. Doesn't a second drogue add a lot of expense? Not really. Because stability is less of a problem, less expensive drogues like the Delta or Seabrake are valid. The rode and bridles are already paid for. Basically, you get the advantages of a series drogue, with more adjustability, flexibility, and easier handling.
The real bargain? It may be a surplus aircraft drogue I bought on E-Bay 15 years ago for $40. To my eye it is just as well built as the Paradrogue, and it gives a lot of stopping force for the buck. Too much for steering, too much for running a bar, but maybe just the thing for parking to drift fish.
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